Method for billing in a telecommunications network

1. A method, comprising:

receiving, from a first session initiation protocol (SIP) device, a SIP call request message for establishing a call with a second SIP device;

identifying a profile associated with the second SIP device;

identifying, within the profile, a call forwarding feature that is enabled for the second SIP device and that identifies a non-SIP device to which the call is to be forwarded;

identifying, based on the call forwarding feature, an authentic originating client as a party responsible for paying for the call;

searching a database to identify a client billing tag that corresponds to the authentic originating client; and

modifying the SIP call request message to include the client billing tag when the database includes the client billing tag.

2. The method of claim 1 , where the call feature includes one of unconditional call forwarding, conditional call forwarding, or find-me.

3. The method of claim 1 , further comprising:

establishing a circuit-switched call connection to the non-SIP device; and

notifying the first SIP device that the circuit-switched call connection has been established.

4. The method of claim 1 , further comprising:

determining that the database does not include the client billing tag; and

denying the call when the database does not include the client billing tag.

5. The method of claim 1 , further comprising:

detecting completion of the call; and

outputting the client billing tag and information regarding a length of the call after detecting the completion of the call.

6. The method of claim 1 , further comprising:

identifying authentication information from the profile; and

authenticating the first SIP device based on the authentication information.

7. The method of claim 1 , further comprising:

adding a security header to the SIP call request message, the security header identifying a server that transmitted the SIP call request message.

8. The method of claim 7 , further comprising:

determining whether the SIP call request message includes the security header;

attempting to establish the call when the SIP call request message includes the security header; and

not attempting to establish the call when the SIP call request message does not include the security header.

9. A computer-readable medium having computer executable instructions for performing a method for placing a call between a first session initiation protocol (SIP) device and a second SIP device, the computer-readable medium comprising:

one or more instructions to receive, from the first SIP device, a SIP call request message for establishing a call with the second SIP device;

one or more instructions to identify a call feature that is enabled for the second SIP device, the call feature identifying a non-SIP device to receive the call;

one or more instructions to identify, based on the identified call feature, a party associated with the second SIP device as a party responsible for paying for the call only when the identified call feature identifies the non-SIP device to receive the call;

one or more instructions to determine whether a database includes a client billing tag that corresponds to the party associated with the second SIP device;

one or more instructions to permit the call to be established when the database includes the client billing tag; and

one or more instructions to deny the call when the database does not include the client billing tag.

10. The computer-readable medium of claim 9 , where the call feature includes one of unconditional call forwarding, conditional call forwarding, or find-me.

11. The computer-readable medium of claim 9 , where the one or more instructions to permit the call to be established include:

one or more instructions to insert the client billing tag into the SIP call request message, and

one or more instructions to output the SIP call request message with the inserted client billing tag.

12. The computer-readable medium of claim 9 , further comprising:

one or more instructions to establish a circuit-switched call connection to the non-SIP device; and

one or more instructions to notify the first SIP device that the circuit-switched call connection has been established.

13. The computer-readable medium of claim 9 , further comprising:

one or more instructions to detect completion of the call; and

one or more instructions to output the client billing tag and information regarding a length of the call after detecting the completion of the call.

14. A system, comprising:

a SIP server to:

receive a SIP call request message that requests that a call be established from a first SIP device to a second SIP device,

identify a calling feature that is enabled for the second SIP device, the calling feature identifying a non-SIP device to receive one or more calls intended for the second SIP device,

determine an authentic originating client based on the calling feature,

obtain a client billing tag that identifies the authentic originating client as a party responsible for paying for the call; and

a network gateway, coupled to the SIP server, to provide at least one of the first SIP device or the second SIP device conditional access to a public switched telephone network.

15. The system of claim 14 , where the network gateway comprises:

a communications interface to establish the call with the public switched network; and

a processor, coupled to the communications interface, to:

receive the SIP call request message from the SIP server,

check the SIP call request message for an existence of a security header appended to the SIP call request message, the security header including a server identifier identifying the SIP server as the server that sent the SIP call request message to the network gateway, and

establish the call based on the existence of the security header including the server identifier.

16. The system of claim 15 , where the processor is programmed to establish the call when the security header exists.

17. The system of claim 16 , where the processor is programmed to not establish the call when the security header does not exist.

18. The system of claim 14 , where the SIP server is to:

forward the SIP call request message to the network gateway if the client billing tag is obtained, and

not forward the call request message to the network gateway if the client billing tag cannot be obtained.

19. The system of claim 14 , where the SIP server is to:

insert the client billing tag into the SIP call request message, and

transmit the call request message with the client billing tag to the network gateway.